Cathode-ray tube

ABSTRACT

APPARATUS FOR AUTOMATICALLY CORRECTING THE POSITION OF AN ELECTRON BEAM EMITTED BY ELECTRON PRODUCING MEANS IN A CATHODE-TAY TUBE EQUIPPED WITH A LINE-SHAPED TARGET AND CONVENTIONAL BEAM DEFLECTING MEANS, WHICH APPARATUS MAKES IT POSSIBLE TO DIRECT THE ELECTRON BEAM EXACTLY ON THE TARGET BY PROVIDING A PAIR OF ELECTRODES FOR DETECTING THE ELECTRON BEAM IN THE VICINITY OF THE TARGET AND BY PROVIDING PAIR OF DEFLECTING PLATES FOR SUPPLYING THERETO AN AC SIGNAL SO AS TO WOBBLE THE ELECTRON BEAM THEREBETWEEN FOR THEREBY RESTORING THE ELECTRON BEAM TO THE PROPER POSITION.

United States Patent [32] Priority Oct. 11, 1967, Oct. 12, 1967, Oct. 13,

1967, Oct. 14,1967, Oct. 16, 1967 3 3 Japan [31 42/65874, 42/66218, 42/66758, 42/6700] and 42/67083 Continuation-impart of application Ser. No. 765,365, Oct. 7, 1968, now abandoned.

[54] CATHODE-RAY TUBE 6 Claims, 10 Drawing Figs.

s2 u.s.c| 315/21, 315/18,:115/26 s1 1nt.Cl H0lj29/70 [50] FieldofSearch 3l5/l8,2l, 26

[56] References Cited UNITED STATES PATENTS 2,523,162 9/1950 Sunstein 315/21 2,710,362 6/1955 Ashby 315/21 3,182,224 5/1965 Stone 315/21 Primary Examiner-Rodney D, Bennett, Jr. Assistant Examiner-Joseph G. Baxter Attorney-Stevens, Davis, Miller and Mosher ABSTRACT: Apparatus for automatically correcting the position of an electron beam emitted by electron producing means in a cathode-ray tube equipped with a line-shaped target and conventional beam deflecting means, which apparatus makes it possible to direct the electron beam exactly on the target by providing a pair of electrodes for detecting the electron beam in the vicinity of the target and by providing pair of deflecting plates for supplying thereto an AC signal so as to wobble the electron beam therebetween for thereby restoring the electron beam to the proper position.

P DISCRI MINA l4 I I0 II i O S C PATENTEI] JUN28 IsII SHEET 3 IF 3 If VA VA A VA RECTIFIER RECTIFIER -1 cArttonaRAv TUBE This invention relates to improvements in a cathode-ray tube and in particular to improved apparatus for positioning an electron beam produced within a cathode-ray tube. This application is a continuation-in-part of my application Ser. No. 765,365, entitled "Cathode Ray Tube, filed Oct. 7, I968 and now abandoned.

While not limited thereto, my invention is particularly applicable to certain forms of a cathode-ray tube equipped with a line-shaped target to which an electron beam is directed, and it is with reference to this application that the invention will be described. The types of a cathode-ray tube to which I refer are that of a cathode-ray tube from which an electron beam is directly extracted into the atmosphere, that of a cathode-ray tube having optical fibers aligned in a file or a plurality of files, and that of a cathode-ray tube for electrostatic printing in which the vacuum side and the atmospheric side of the vessel are connected therewith by way of conductive wires. Those cathode-ray tubes are equipped with a conventional electron gun for producing and emitting an electron beam towards the line-shaped target. ln addition there are provided, in the path which the electron beam follows between the gun and the target, a pair of detecting electrodes which are insulated from each other and are disposed in the vicinity of the target at a distance of nearly the width of the target, and a pair of deflecting plates which are disposed in substantially parallel relation with the target and are given both the wobbling signal for causing a slight oscillation of the beam in the direction of the width of the target and the correcting signal of the beam position. As is well known, if both of the deflecting plates are maintained at the same potential, the beam will trace upon the line-shaped target a path defined only by the orientation of the electron gun and of the conventional horizontal and vertical deflecting means with which the cathode-ray tube may be equipped. If, on the other hand, a potential difierence is developed between the deflecting plates, the beam is additionally deflected upward or downward depending upon the polarity of the potential difference. in utilizing a cathode-ray tube of the foredescribed types as the image reproducing device of a facsimile receiver, the geometries of the beam deflecting plates and the detecting electrodes are so coordinated with the geometry of the line-shaped target structure, and a slightly varying potential difference is so applied between the deflecting plates that the electron beam slightly oscillates or wobbles therebetween so as to impinge, in a certain sequence, upon the target. At the same time, the beam intensity is controlled by means of a signal which represents, during successive time intervals, modulation intelligence applied thereto.

It should be noted here that a practical target structure may be about 25 cm. long and less than l;l.m wide. Since the target must have these approximate dimensions to improve the resolving power and to increase the relative strength for pressure difference, it is quite difficult to direct the whole electron beam correctly upon the target. At present, an electron beam is easily formed with less than several pm in diameter, and then it is sometimes desirable to make the width of the target of the same order. Accordingly, difficulties tend to occur such that the substantial portion of beam does not impinge upon the target correctly or that the beam striking it lacks uniformity, when the beam departs from the target during scanning or when it stays away from the target during wobbling.

It is, therefore, a primary object of my invention to provide improved apparatus for a cathode-ray tube equipped with a line-shaped target, which apparatus is responsive to the electron beam emitted by electron producing means and activates deflecting means which is, in turn, effective in automatically positioning the electron beam.

It is another object of my invention to provide improved apparatus equipped with a pair of detecting electrodes for sensing the deviation of the electron beam and with a pair of deflecting plates for deflecting the electron beam passing thereby, which plates are given both the wobbling signal and the beam position correcting signal.

It is still another object of my invention to provide improved apparatus, in which a pair of said electrodes are fabricated integrally with the narrow target beforehand so as to coordinate the geometry of said electrodes with that of said target.

The construction of apparatus which achieves these objects, as well as others which will appear, is predicated on the realization that the type of cathode-ray tub e under consideration is equipped with a pair of detecting electrodes and a pair of deflecting plates. in addition, I provide a pair of AC amplifiers of narrowband type, which are connected with the electrodes for the purpose of amplifying each of the detected output signals appearing thereon, an amplitude composer which is connected with the two amplifiers for composing the outputs derived therefrom and for producing the output of itself when the beam is deviated from the target, and a phase discriminator for discriminating the phase of the output wave form composed by the composer and for supplying a voltage corresponding to the amplitude of the output signal thereof to the deflecting plates. In another embodiment of my invention, I provide a pair of rectifiers for rectifying the two output signals derived respectively from each of the amplifiers, and a comparator such as a difference amplifier for comparing the two rectified signals and for applying a voltage corresponding to the output signal of itself to the deflecting plates.

With respect to the essential features of my invention, it is desirable that the perpendicular oscillation or wobbling has a fixed frequency which is higher than that of the intensity modulation of the electron beam, and that the amplitude of the oscillation is made in such a manner that only a small portion of the electron beam strikes each of the electrodes alternately. The detecting electrodes, however, are not necessarily required to collect the beam but may be of the type that an electrostatic induction can be used. It is also essential to fabricate integrally the electrodes with a line-shaped target beforehand so as to make the centers of the two to coincide correctly therebetween.

Since the signal detected on the electrodes is an AC signal with a fixed frequency, my invention is definitely advantageous in that a narrow-band frequency selective amplifier can be used, which has low noise and high intensity, and in that a quick response is obtained because of the phase detection of the deviation of the electron beam.

The above objects, as well as other objects, features and advantages of the apparatus of the invention will be more clearly understood in view of the following description when taken in conjunction with the accompanying drawings hereinafter, wherein:

FIG. 1 is a longitudinal sectional view of a cathode-ray tube equipped with a line-shaped target;

FIG. 2 is a front view of the cathode-ray tube shown in FIG.

FIG. 3 is an enlarged sectional view showing the main portion or beam detecting block structure of the cathode-ray tube, wherein a pair of electrodes are disposed to detect the electron beam in the vicinity of a line-shaped target;

FIGS. 4a and 4b illustrate how the electron beam moves between the two electrodes when it is scanned or when it wobbles, respectively;

FIG. 5 illustrates one embodiment of my invention showing a longitudinal sectional view of an apparatus for use with a cathode-ray tube for correcting automatically the electron beam to its proper position by processing the signal produced by the electron beam collected or detected on the two electrodes and by returning the processed signal to the deflecting plates of the electron beam;

FIG. 6 shows signal waveforms which appear in the circuit shown in FlGS. 5 and 7; and

FIG. 7 illustrates another embodiment of my invention showing a longitudinal sectional view of an apparatus for use with a cathode-ray tube.

Referring now to the accompanying drawings, the following description will be limited for brevity to the simple case in which a cathode-ray tube is of such a type that the electron beam is extracted into the atmosphere therethrough'FlGS. l

and 2 show the longitudinal section and front view, respectively, of a cathode-ray tube equipped with a line-shaped target. Not shown are conventional horizontal and vertical deflecting means of the electron beam, and electric circuits. Also not shown are a pair of detecting electrodes and a pair of deflecting plates. In short, a cathode-ray tube shown in FIGS. I and 2 may be considered a conventional one, which includes a thin film I, supporters 2 and 3, a glass envelope 4 and a conventional electron gun 5. As a result of the action of the electron gun S the electron beam is produced, which is deflected horizontally and vertically in response to the fields when the conventional deflecting means are energized. The electron beam flies toward the line-shaped portion of the thin film I enclosed by the supporter 3, which are disposed for reinforcing the thin film l. The supporter 2 has holes in the shape of a mesh or a lattice, and the supporter 3 is a base which encloses the thin film 1 like a frame and forms a line-shaped target. Moreover, a glass envelope 4 is a conventional one to hold a vacuum within the cathode-ray tube.

In order to improve the resolving power of a cathode-ray tube and at the same time to increase the relative strength of the thin film I, a portion of it enclosed like in a frame by the supporter 3 must be necessarily narrow in width. Furthermore, the electron beam is easily formed with less than several am in diameter, and it is sometimes desirable to make also the width of the target of the same order. As a result, when the electron beam is scanned along the narrow target in its longitudinal direction, such difficulties may often occur that the electron beam does not hit the target correctly or the very beam lacks uniformity although it hits the target. Those undesirable difficulties are considered to occur when the electron beam departs from the target during the scanning or stands outside of the target. According to my invention, however, the position of an electron beam is sensed by a pair of electrodes provided in the vicinity of the target. The construc tion ofa beam detecting block is shown in an enlarged view in FIG. 3 and will be explained at greater length hereinafter.

Referring to FIG. 3, a pair of electrodes are disposed oppositely to each other in the vicinity of the thin film I at a distance of nearly the width of the enclosed portion thereof, say, the width of the target. The centerline of the spacial distance bordered by the two electrodes 6 and 6' must coincide with that of the target portion of the thin film l as is apparent from the sectional view of the cathode-ray tube. Moreover, reference numerals 7 and 7' are electrode supporters, which are made of an insulator while the electrodes are made of a conductor as is the case of FIG. 3. In this instance, two important factors regarding the electrodes must be considered: one is their geometry and the other is the distance between them.

With respect to their geometry, the coincidence of the centerline of the space bordered with the two electrodes with that of the target is very important. Therefore, the two electrodes must be previously constructed in another block or the beam detecting portion and, thereafter, the block is bound or secured to the glass envelope 4. The reasons why the electrodes must not be attached directly to the glass envelope 4 are that it is difficult to fit the electrodes in the correct position with a suitable jig when the electrodes are disposed on the side of the glass envelope 4, and that the position of the electrodes adhered to the glass envelope 4 may change due to sliding during the hardening procedure. Therefore, it is essential to fabricate integrally the electrodes within the block beforehand.

With respect to the distance between the two electrodes, on the other hand, it may be practically about 0.5 to L times the width of the target. As has been described before, when the whole electron beam does not hit the target by the screening action of the electrodes. namely, only a small portion of the electron beam impinges upon the electrodes, the detection sensitivity of the electrodes can be improved substantially although the utilization efficiency of the beam falls down. When the electron beam is not caught hy the electrodes. on

the other hand, the utilization efficiency of the electron beam is augmented to a high value in spite of the reduction of the detection sensitivity thereof. Therefore, good results can be expected if the width of the space between the electrodes is about 0.5 to L5 times that of the target, according to my experiments.

In FIGS. 40 and 4b. the behavior of the electron beam 12 is illustrated so as to aid in visualizing how the electron beam 12 moves when it is scanned not along the narrow space bordered with the two electrodes 6 and 6 as shown by the dotted lines or when it wobbles perpendicularly to the width of the narrow space as shown similarly by dotted lines, respectively. It should be noted here that FIG. 4 also illustrates another important function of my invention. As has been described beforehand, it is desirable that the perpendicular oscillation or wobbling of the electron beam 12 is given a fixed frequencyf which is higher than that with which the intensity ofit is modulated. Furthermore, the amplitude of the perpendicular oscillation is made preferably in such a manner that only a small portion of the electron beam 12 strikes alternately the two electrodes 6 and 6', as is apparent from FIG. 4b.

The construction and arrangement of the apparatus embodying my invention will now be described with reference to FIG. 5, wherein attention is paid to the way the electron beam is affected and controlled. Parts identical to those in FIGS. I to 3 are identically numbered and will not be described further. Numerals 8 and 8' are electrostatic deflecting plates for supplying thereto the wobbling signal and the voltage signal for correcting the position of the electron beam passing thereby. These plates are positioned oppositely to each other in the cathode-ray tube on the side of the target which is remote from the electron gun. The arrangement of them is less critical so that they need not be formed integrally with the supporting block 3 beforehand. A shielding plate 13 is also disposed in the tube, which plate prevents the electron beam from striking directly the deflecting plates 8 and 8'. Conductive caps 14 and 14 are affixed to the envelope 4 for connecting the deflecting plates 8 and 8' with the electric circuit, which will be explained in detail in conjunction with the operation of the apparatus. Conductive caps I5 are attached to the envelope 4 in order to ground the shielding plate 13 electrically. Numerals I6 and 17 are deflecting means of a conventional type, such as an electromagnetic deflecting coil and an electromagnetic focusing coil, respectively. With respect to the electric circuit, provided are narrow-band selec tive amplifiers 9 and 9', an amplitude composer I0, a phase discriminator II and an oscillator I8 in the circuit all for automatically controlling the position ofthe electron beam.

When the electron beam oscillates as shown in FIG. 4b by the action of the signal given by the oscillator I8, a pulsating current having the wobbling frequencyfas its principal component is produced between the electrodes 6 and 6'. By amplifying the pulsating current with the narrow-band selective amplifiers 9 and 9', sinusoidal waveforms as shown in FIGS. 60 and 6b are obtained. In this instance, FIG. 6 will be explained for illustrative purposes. It will be assumed here that FIG. 6a shows an output waveform of the amplifier 9 and that FIG. 6b shows an output waveform of the amplifier 9'. The waveforms of FIGS. 6a and 6b have a phase difference of between them. FIG. 6 presents a case in which the amplitude shown in FIG. 6a is larger than that shown in FIG. 6b, which means that the electron beam is scanned closer to the electrode 6 than to electrode 6'. A waveform as shown in FIG. 6c is obtained by composing the two waveforms of FIGS. 6a and 6b by the use of the amplitude composer 10. Accordingly, when the amplitude of the waveform of FIG. 6a is equal to that of FIG. 6b, that is, the electron beam oscillates symmetrically along the centerline of the space between the electrodes 6 and 6', the output of the amplitude composer I0 as shown in FIG. 6c becomes zero. The frequency of the oscillation perpendicular to the width of the space between the two electrodes is higher than that of the intensity modulation supplied to the beam, as has been described before. Consequently, the electron beam can be put back in its proper position upon the target by discriminating the composed waveform shown in FIG. 6c by the operation of the phase discriminator ll and by supplying a voltage corresponding to the amplitude of the output signal of the phase discriminator ll to the deflecting plates 8 and 8'. As a result, the electron beam is deflected vertically, say, upward or downward to the correct position of the target. The definite advantages of such a method as described hereinbefore are summarized as follows:

I. Since the signal detected on the electrodes 6 and 6' is an AC one having a fixed high frequency, a narrow-band frequency selective amplifier with low noise and high sensitivity can be used.

2. A quick response can be obtained because the deviation of the electron beam is sensed by using the phase detection.

FIG. 7 shows another embodiment of my invention, in which only the electric circuit is different from that of the embodiment as has been described with reference to FIG. 5. In this case, the two output signals respectively derived from each of the amplifiers 9 and Q are first rectified by rectifiers l9 and 19', then they are compared to each other with a comparator 20 such as a suitable difference amplifier, and finally they are supplied as a signal from the comparator 20 to the deflection plates 8 and 8' for correcting the position of the electron beam.

It should be appreciated that, in the aforementioned description, a small portion of the electron beam must necessarily strike the electrodes 6 and 6' during wobbling in the perpendicular direction of the target for ensuring the detection sensitivity. When the beam is considerably deviated, it is necessary to increase the wobbling amplitude to such an extent that the signal can be obtained from both of the plates, and next the perpendicular amplitude is gradually decreased during the correction of the beam position. The electron beam is also scanned in the lengthwise direction of the target by the sawtooth signal signal of the conventional electromagnetic deflecting coil 16, so that it is, of course, possible to employ as a deflecting source of the beam the signal ofa low frequency with which the intensity of the beam is modulated. Therefore, without wobbling the beam, it may be sufficient for the AC amplifiers 9 and 9' to be responsive to the band of the sawtooth signal. In this instance, the difference in the output voltages from the amplifiers 9 and 9' is directly returned to the deflecting plates 8 and 8' with good results, in spite of the fact that a quick response of the operations, say, one of the preferable features of my invention is inevitably sacrificed.

After all, the beam deflecting apparatus according to the present invention is summarized in the following description. in a cathode-ray tube equipped with a line-shaped target a pair of electrodes are provided for detecting the electron beam, which electrodes are disposed oppositely to each other in the vicinity of the target at a distance of nearly the width of the target, and a pair of electrostatic deflecting plates for correcting the position of the beam, which plates are disposed either oppositely to each other in substantially parallel spaced relation to each other and are located closer to the electron gun than the electrodes so as to supply thereto both the beam position correcting signal produced by the difference in the two detected outputs and the wobbling signal for causing a slight oscillation of the beam in the direction of the width of the target. Furthermore, the signals detected on the electrodes are those having a fixed high frequency, and are in the first case discriminated through the phase thereof. As a result, the electron beam can be correctly directed onto the narrow target automatically with high sensitivity and quick response. Therefore, it is further possible to reduce the width of the target considerably, so that high resolving power of the cathode-ray tubemay be attained when recording or other operations of the tube are carried out.

It will be understood that still other embodiments and applications of the beam deflecting apparatus according to my invention will be formed by those skilled in the art. Consequently, I desire the scope of my invention to be limited only by the appended claims.

I claim:

1. Apparatus for automatically correcting the position of an electron beam emitted by electron producing means in a cathode-ray tube equipped with a line-shaped target and conventional beam deflecting means, which apparatus comprises:

a pair of detecting electrodes for sensing the deviation of the electron beam, said electrodes being insulated from each other and disposed oppositely to each other in the vicinity of said target at a distance of nearly the width of said target, and the geometry of said electrodes being coordinated with that of said target,

a pair of deflecting plates for deflecting said electron beam passing thereby, said plates being disposed oppositely to each other in substantially parallel relation to each other and located closer to said electron producing means than said electrodes for the purpose of supplying thereto both the beam position correcting signal produced by the difference in the two output signals detected on said electrodes and the wobbling signal having a fixed frequency higher than that of the intensity modulation of said electron beam so as to cause a slight oscillation of said electron beam in the direction of the width of said target.

2. Apparatus as set forth in claim 1, wherein;

said electrodes are energized by said electron beam, a small portion of which is made to impinge alternately thereupon with the wobbling amplitude, and

said deflecting plates use electrostatic induction so as to deflect said electron beam according to the potential difference developed therebetween.

3. Apparatus as set forth in claim 2, further comprising a pair of narrow-band selective AC amplifiers respectively connected with said detecting electrodes for the purpose of amplifying each of the detected outputs appearing on said electrodes and an oscillator connected with one of said deflecting plates for the purpose of applying the wobbling signal to said deflecting plates.

4. Apparatus as set forth in claim 3, further comprising an amplitude composer for composing the two output wave forms derived respectively from each of said amplifiers for thereby producing the output signal ofitself when said electron beam is deviated from the proper position on said target, and

a phase discriminator for discriminating the phase of the output wave form composed by said composer and for applying a voltage corresponding to the amplitude of the output signal of said composer to said deflecting plates.

5. Apparatus as set forth in claim 3, further comprising a pair of rectifiers respectively connected with each of said amplifiers for rectifying the two output signals derived respectively from each of said amplifiers thereby producing the two output signals of themselves and a comparator for comparing said two output signals rectified by said rectifiers and for applying a voltage corresponding to the difference between the output signals of said rectifiers to said deflecting plates.

6. Apparatus as set forth in claim 1, wherein said electrodes are fabricated integrally with said target beforehand so as to coordinate the geometry of said electrodes with that of said target. 

